I am not trying to solve any particular problem, but trying to learn R and understand its logical negation operator "!" documented on page http://stat.ethz.ch/R-manual/R-devel/library/base/html/Logic.html
It works for me when used in combination with =, in expressions such as:
1 != 2
TRUE
But I can't quite comprehend standalone application of this operator. For instance, can I use it to select elements of the list which do not have specific name. Here's my attempt to do that, but it did not work:
vector1 <- 1:5 # just making vector of 5 numbers
vector2 <- 5:1 # same vector backwards
list <- list(Forward=vector1, Backwards=vector2) # producing list with two elements
x = "Forward"
list[!x]
My output is:
Error in !x : invalid argument type
Will appreciate any hints on where my logic goes wrong in this case, and what are other good uses of this operator except for != case.
Thanks! Sergey
First, it's probably best not to think of !=
as !
acting on =
, but rather as a separate binary operator altogether.
In general, !
should only be applied to boolean vectors. So this is probably more like what you are after:
vector1 <- 1:5 # just making vector of 5 numbers
vector2 <- 5:1 # same vector backwards
l <- list(Forward=vector1, Backwards=vector2) # producing list with two elements
x = "Forward"
l[!(names(l) %in% x)]
where names(l) %in% x
returns a boolean vector along the names of the list l
indicating whether they are contained in x
or not. Finally, I avoided the use of list
as a variable, since you can see it is a fairly common function as well.
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